Tennis balls



July 28, 1959 H. c. L. DUNKER TENNIS BALLS Filed March 15, 1954 2 Air of atmospheric pressure.

\ 4 Resinous high styrene-butodiene oopolymer and rubber.

2 Air at atmospheric pressure v 4 Porous resinous hi h st rene copolymer ond r bbe ATTQRNE YS United States Patent Henry- Ghristianioui's Drinker, Halsingborg, iSweden .AmilicatiouMarchf-fiy 4, Serial Nil-#41163 Claims priority, application Sweden August 22,1950 -11':Claims.. :(l..7:3-61) This appli at o iis a c ntinnat enin part of applicants -P app c ion ."Seriial fNo- '238',;1 Z,.fi1edfIuly 1951, and Serial No. 266,443, 'fil'e'd January 24', 1952, both now abandoned.-

The presentinvention relates to improvements in tennis balls.

Ordinary tennis ballsgenerallyeonsist;of;an;inner.hollow core of rubber ,(rubber ball) having a .gas fi11ir 1g:.under super-atmospheric pressure .anda coveringof, felt. attached =to theoutside ,of, said.core., .The structuralcharacteristics of the ball,, such ,as, the composition of .thesrubber, :the wall thickness and the diameter ,of .the. rubber. tame, @-the amount ,of super-atmospheric pressure, and .the: nature of the felt covering, may be varied within relatively ,narrow limits since these characteristics are required ;to impart predetermined properties to the ball with respect to the outer diameter, weight, hardness and rebound.

These requirements are defined in "the Rules ofLawn Tennis as laid down by;the InternationztlTennis Federation. According -tothese: specifications, 'a-tennis 'bal'l shall be more t-han 2 /2 inches and less thanZ /s' inches in diameter, and not less than 2 ozs. (56.7 gr.) nor more than '2 A ozs. (581-5 gr.) in weight, and the ball shall have a minimum reboundof 53 inches (135 cm;) and a maximum rebound of 58 inches (147 cm.) when dropped l-GOfinches '(25'4-cm.) and a deformation of. notless than 2650f an inch andinot more than .290 of an inch when subjected to a pressure of' 1'8 'lbs'.

In ,a tennis ball' which'is' made so as to comply with the requirements of diameter and weight, the proper hardness ,and rebound properties are general y attained by suitably adjusting the super-atmospheric pressure of the gas filling within the rubber core. However, the finished ball will not keep these ,properties ,unchanged for any considerable period of time, because ,the ,gas under' pressure gradually ,difiuses out through the .rubber wall, and thereby results in a reduction of both the hardness and the-rebound of the ball,

Attempts have .already been made .to avoid .these ,dilficulties by varying the pressure of ;the gas filling and by increasing the impermeability of the ruhbeneovering. F e mple, t h een-proposed tostifien the rubber core by means of ,a network ,of ,ribs on :the interior surface thereof. However, none of the proposedsolutions to the problem of storage has'been successful in practice;

'The principalobjectof the present invention i's'to provide an improved "tennis ball in which the require- "ment of havinga gas filling of super-.atmospherie pres sure is dispensed with and which, owingto the' absence :of apressu-re differential between the inside and outside of the modified rubbercore, .willmaintain .itsori'g nal proper hardness and rebound properties for alongperiod of time.

It is a further object of the invention to provide a tennis ball comprising a hollow modified rubber core having an outer diameter'and 'awailthickness"similar to a W 2,896,949 ,PatentedaJ-uI-y28,11,959

those of tennis balls in general .use but'zcontainingzaogas filling at atmospheric pressure, whilendisplayinga. vquired hardness and .rebouridmroperties.

Another. object of thainventionais: to: provide :a :tennis ball comprising a hollow modified.'rubheracorencontaining agas filling atatmosphericapressure, and.an outer'ifelt covering, said'ball beingv similar: intappearanee and :playing properties to atennisgballsrlwhich satisfy "theiImten national and National Tennis Associatihnuneqniremenis but having;substantially;improvedkeepingtqualities and", as a consequenqe: t-hereo f, 1a, pnolongedzplaying ilifer A further object ,of xtheinvention; isntovprovidexaxtennis ball comprising achollow modified rubber-georecontetiningsa .gas filling; at. atmospheric:eprlessnre;.zandz:an iouter covering serving to 1give theball;the;surfiaizercharacteristics required in oflicial match :play, gsaid ball ihei'ng capable of being stored; for;aprolongedrtime;periodiwithout any falling-off intitszhardnesstand rebound properties.

.According to the present, :invention, :the :above and other objects ,fl z :attained {in :artennis .ball, comprising a hollow rubber structure by :having incorporated -in =said ,structlme an ingredienhconsisting of auresinous hi styrene butadiene ,copolymen.

Theaeeompanying drawingdlhistrateszexamples=of ten nis halls in. accordance .with: :the iPIQSeDt :invention. Figures. :1 ltoqS, inclusive sholwxcrosssections :of tennis :balls till accordance with. 511136 invention.

.In -Figures -.-'1- 3f, the tennis: :ball icomprises a molded and ;cure.dsrlihber composition 4 .eont-aining rubher, rubtber processing ingredients and a high styrene-ibutadiene copolymer, the "ball i-being ifilled 'with :a gas 2* at? stantiallyratmosphericzpressure, In Figs I' and 3 2 cov- ;ering;of.textile-mateiial ids-shown. In Fig. 2a covering :cflsponge irubber .3' is shown,

In Figs. 1 and 2, the tennis ball comprises a d'uril layered structure, the: inner".:1ayer"1' being made from a. molded :and rcured rubber composition of the wel'lfknownutype land the outer ilayer 4 being composed' o'f a composition of. rubber, rubber processing ingredients, and. a: high styrene -ibutadieneicopolyrner. A surfacedayer .or covering, 3 .of felt Eis. applied to said rubber structure. Figure '4 illustrates aldetail of atenni's ball' in amodification of :Eig. 3f, athevd'etail' consisting of a inal layer rubberrstructure, .in'which the: inner layer 7 'is 'composetl of :an ordinary rubber composition and the. outer layer 8 of a rubber :composition including a high styrenebutadiene copol-ymer, said outerlayer 8 being of'a' spongy character, so that no. feltcover ing' is needed.

Resinous'copol-ymers of styrene and hutadiene eman- :ingsat least 50% by weight of-styrene are known to'st ifi'en rubber. lit'has been :found that t hey increase the hardness and rigidity .of'the rubber stock. In.generallhthey also improve the tens'il'e strength, itoug'hness, and-resist ance to tear and abraSion-ofrubber; "Therefore, such copolymers 1'1B.V6' bBe11 found useful as stilferiing and "reinforcing agents in -rubber soles and similar articleswhere the hardness andabrasion resistance of the rubber of primary importance, inter aliain 'go-lfball, soft ball and basketball covers.

Applicant has found by incorporating such resinous hjgh styrene-butadiene copolymers in the'rubber "struc- 'ture of tennis balls that properly-matched hardness and rebound characteristics o'fthe finished "balls mayj-be pro duced in the absence 'ofsuper-atmospheric gas pressure filling within the hollow rubber" structure. On'the of the knowledge-of theinfluence of" such 'copolynr'ers on the'properties of' rubber stock, it'was'tobeexpected that an increased hardness of the rubberstructure balls wouldresult -from1'the incorporation ofthecopdlymers' in "the-rubber; A similar increase in 'hardness'is observed upon adding such well-known ingredients to the rubber, as inorganic fillers such as kaolin or chalk. It was surprising to discover, that despite an increase in hardness the remaining resilience of the rubber stock is remarkably effective in tennis balls to permit the objectionable super-atmospheric pressure within the balls to be dispensed with. Particularly, in view of the reduction in the resilience of the rubber caused by the coplymer, it was not expected that tennis balls made from such rubber stock and having a gas filling of atmospheric pressure could possess the proper weight and hardness and also comply with the requisite rebound specification under the international rules.

One example of a resinous high styrene-butadiene copolymer'which is suitable for the purposes of the present invention is a product sold by the B. F. Goodrich Chemical Company under the trade name of Goodrite Resin 50 and consisting of about 85% styrene and 15% butadiene. Thi resin is described for example in an article Rubber or Plastics in the Modern Plastics, July 1948. Other examples are a product sold by the Marbon Corporation under the name of Marbon B and a product sold by the Dewey and Almy Chemical Co. under the name of Darex Copolymer 3, both consisting of 70% styrene and 30% butadiene. A further example is a product sold by the Polymer Corporation, Ltd., of Canada, under the same of 58-250, and consisting of 55% styrene and 45% butadiene. Still another example is a product sold by the Goodyear Tire & Rubber Company under the name of Pliolite 8-3. The important characteristics of this product are explained in an article Styrene-Diene Resins in Rubber Compounding by A. M. Borders et al. in the Industrial and Engineering Chemistry, vol. 38-l946. Further examples of suitable copolymers are products sold by the Marbon Corporation and known under the names of Marbon S and S1, vwhich are described in an article High Styrene Resins in Rubber Compounding by A. G. Susie et al. in the Rub ber Age, August 1949.

A tennis ball embodying the present invention may consist of an inner hollow rubber body having uniformly incorporated therein by conventional rubber handling procedures a high styrene-butadiene copolymer and an outer covering of the usual felt material or a material having characteristics equivalent to those of such felt material, such as sponge rubber, the said body enclosing a gas filling, preferably air at ordinary atmospheric pressure. The rubber blend from which the said rubber body is made may, apart from ordinary fillers and processing ingredients such as kaolin, accelerators, and sulphur, preferably contain from about 65 to about 90 parts of rubber and from about 10 to about 35 parts of a high styrenebutadiene copolymer. Where a copolymer very high in styrene, e.g. containing about 85% styrene and about .15 butadiene (Goodrite Resin 50"), is used, an amount of said copolymer at the lower part of said range is required, whereas a copolymer lower in styrene will as a rule be added to the rubber in amounts nearer the upper limit of said range, in order that the finished tennis balls shall have the desired hardness and rebound properties. However, the application is not restricted to the exact ranges of the constituents mentioned above, since these may be varied somewhat so that the proportions may sometimes be a little outside of these ranges.

It is to be understood that the amount of resinous high styrene-butadiene copolymer incorporated with the rubber is an amount suflicient to prevent the resilience of the finished ball from dropping below a minimum value which will reduce the rebound properties as are necessary to comply with the Lawn Tennis specification, and at the same time the amount is sufiicient to render the core substantially impermeable so that it will have the compressibility, hardness, wall thickness and weight characteristics despite modification by conventional filler ingredients.

In a laminated core construction the copolymer rubber mix may be even higher in copolymer content in the inner core to produce a tennis ball meeting the Lawn Tennis specifications and having the same unexcelled storage characteristics as the single layered core. Further, the single layered core modified at its surface with a blowing agent possesses such an excellent balance of properties within the specification requirements so that the usual felt covering may be entirely dispensed with.

The characteristics of the finished balls are only slightly influenced by varying other factors, such as the proportion of kaolin or other filler in the rubber blend and the processing operations, mastication, rate of curing, etc.

' The wall thickness of the rubber body, and the nature of the outer covering are as required for the hardness and rebound specifications as are also the weight and diameter of the balls.

A typical example of a rubber-copolymer composition within the above-mentioned limits which may be used for making tennis balls as described is as follows:

EXAMPLE 1 Parts by weight Rubber 100 Resinous copolymer styrene, 15 butadiene) 30 Zinc oxide 5 Kaolin 20 Stearic acid 2 Accelerator 1 Sulphur 2.5

The rubber blend is processed as is usual in rubber manufacture, and the ball cores are made therefrom using any well-known forming and curing technique except that the means for developing super-atmospheric pressure within the cores are dispensed with. The appli cation of the outer covering of felt material or any other equivalent material is also carried out in the well-known manner.

It is within the purview of the invention to produce tennis balls in which the hollow rubber structure includes an inner hollow rubber core containing a gas filling of atmospheric pressure and a rubber layer surrounding said core and having the resinous high styrene-butadiene copolymer incorporated therein. Since the said rubber layer containing the copolymer is here relied upon to impart to the balls the necessary hardness and rebound properties, otherwise obtained by having the gas filling at super-atmospheric pressure, and since this layer constitutes only part of the thickness of the rubber structure as a whole, the range of percentages of the copolymer in the rubber of said layer will be moved upwardly to some extent. For example, in using a copolymer containing 85% styrene and 15% butadiene (Goodrite Resin 50) at least 15% of this copolymer may have to be included in the rubber blend, and in using a copolymer containing 70% styrene and30% butadiene (Marbon B) the proportion of copolymer in the rubber blend may be increased towards 50%. Typical examples of rubber-copolymer compositions which may be used for this variety of tennis balls are as follows (the figures being parts by weight):

Example" 2 3 4 The rubber blends, after being processed, are preferassets ably formed-into sheets: in :a pressure curing operation carrieduont ina wellahnown manners *From these: sheets th'en stamped piecesof a desiredgshap'e which :are

coated with a cement and applied as a covering around .the inner cured rubber core. I

'The: hollow rubber structure, comprising the inner -holl'owrrubber core andthe outer covering :of a :rubbermaking an additional felt surfiace layer superfluous. lihewcovering-may be made spongy by adding 'to the -mhber-copolymer compositions, 'for example those mentioned :as .Example'Nos. '2, 3 and 4' above, so called agents, ez'g. ammonium carbonate, =bi'rcarbonate (of soda, ammonium :nitrate, az'o compounds tsomethnes :used under :the trade names of' Unicelg *Vlilkaeel, Porofor, etc.) and others, in amounts of about 6 to=7 parts in the formulas of Examples 2, 3 and 4. Owing to the gases which these substances-release on heating when the rubber is cured, the rubber becomes more or less spongy. The sponginess ofthe eovering-makes ,it lighter and reduces the rebound and hardnesscharacteristics of the tennis balls, which has to betalien into account in designing the rubber structure. Thus, by varyingt-he composition o the=rubber copolymer blend particularly the ratioofrubber to copolymerand the ainountor blowing agent, the rebound and hardness of the finished tennisballs may thereby be effectively controlled.

To illustrate the improvement achievedtby the invention a number of rubber compositions and tennis" alls made therefrom, filled atatmospheric pressure have been tested, and an account thereof -iS-,giVI below. Int-hose tests the rubber blends of various compositions are ,mixed with various proportions of a high styrenerbntap diene copolymer or other ingredients (cyclized rubber, coumarone resin, or kaolin), the hardness and resilience of the rubber made from such rubber-copolymer mixtures are determined, tennis balls are made from these rubber mixtures, and the compression (the inyerse-lofifliardness) and the rebound of the balls determined. The hardness of the rubber mafe'ri'ahis determined by means of the well-known Shore durometer A, and the resilience is 'teste'dbymeans of aSchob pendulum in which the degree of resilience of the t'estgpieceisntieterminedby the, rebound of the pendulum aaftertalling' down onto said piece, the

test valtle expressed in percentof the-total --fall-offthe" balls by "apredetermined load is measured in thousands of inches.

L-C0mpara1ive tests of rubber mixed with tvariozas amounts #0) high. .styrene-butadiene copolymer" tor .nyclizeirubber iI-Iigh styrene fbutadiene copolymer (Gpodrite Resin 25.0 and-Lcyclizedz rubber; respectively, was mixed with jaqrubber'tzblend of the following; gompositgion in paints by wisht:

, 36., remains- 1A.

The rubber mate al the bars hallfsp ss we e tested as explained above. 7

The results are given irr'th'e following Tables I and II.

raster Rllbberzeompound-i u stwmnprbumlenp Oycllged rubber Rubber admixture copolymer i Hardnes riteslllenee Hardness #3981119? I l V s oi as p0, L Q0 $15: 69 1 358 6%- "52 9... .82. ..3.

TABLEHII [BallemsdeztromaSfi parts mbbnr-iwpartestyrene-butadiene eopolymer oncyclizedfrnbbenj Copolymer Cyellzed rubber i'Rahmmrl 110.v l @1 50 .Eompresslon=.- 3'05 Weight, g. .1.

The rubber blendeentained-a -relatively high -percentage :ofi 'ikaolin; results indicated in arable: I=.'.show that .bysuhstitutinghigh: stynenerhutaifiene for :part: the :rubber atrubber' material havingoipcrensedzhandness reduced IEBSliiCBQQAQfiH ihe tolatailieth. :zlh'tcompaaiison, -cycjlizrd rubber, :gives :alnmos'treanalincreasesin;rh'ardi ness =hutza greater reduction resiliencet: :rFrom II it may be seen that a ball in which the rubber material contains 15% oopolymer, calculated on the basis of rubber+copolymer, has properties which might make it suitable as a tennis ball, while a ball having part of the rubber replaced by cyclized rubber appears to be less suitablebecausethe rebound has dropped too much. (The bare ball cores, such as tested, ought to have slightly greater amounts of rebound and compression than required for v; t h; :finished balls.)

IL-Investigation 70 the connection between hardness and resilience -of--rubber-and rebound and compression of .balls made. .t-herefromf The rubber blendsnsed in these experiments diflered slightly from those employed in the experiments reported under -I-. 1

A-first series -of-runs-'were conducted with two different rubber blends mixed with high styrene-butadiene copolymer (Goodrite Resin 50). The formulas of these blends are given below, and the results are summarized in the corresponding Tables III and IV for various amounts of high styreneabutadiene copolymer.

a5 FORMULA B Natural.rubber,,.,. ,Zinc carbonate 10 Kaolin 10 I Stearine 1.5

'R'os'in .5 Mineral oii v Mercaptobenzothiazole 1.6 El p r sufalti.id ne .uLSulphur 3Q FORMULA which isv clearly seen in Table HI. The bareball cores Natural rubber I 100 also dlsplay a maximum of rebound at a content of about 1O to copolymer 1n the rubber, which confirms the ar nat --r-.--a

5 fact that good resilience of the rubber is of importance Kaolin 2 Starine L5 5 for the rebound of the ball. With such low copolymcr R 5 content, however, the compression of, the ball is much 05m 7 Miner a1 oil 5 too high. To produce a. ball having the desired prop- Mercaptobenmthiaz 01 e L6 erties and not contaimng a gas filling at super-atmosphenc pressure a rubber-copolymer mlxture contalnmg D1phenylguan1d1ne 1 1.8 Sul but 3 O 10 a h1gher proportion of the copolymer is used while tak- P n ing into account that the rebound is reduced at the same TABLE III time, and all the more as the amount of kaolin in th rubber blend is increased. Rubber-i-Styrene- Bare ball core Other series 0f runs were carried 01111 With additional R Styrene" Butadiene oplymer rubber blends according torthe following Formulas D, E,

ubberin butadiene FormulaB copolymer and F m1xed with various proportions of kaolm, cou- Hardness Resilience 33 Rebmmd marone resin, or high styrene-butadiene copolymer (Goodrite resin 50), respectively. In these experi- 0 50 66 -70O 180 ments the compression, the rebound, and the weight of 10 w h 69 70 660 186 the bare ball cores, on the one hand, and the finished g g g2 (felt covered) balls, on the other hand, were examined. 35 86 47 71 130 The results are found in the following Tables V VI d VII an T N FORNIIIL'A D 5 Natural rubber 100 Zinc oxide 8 Rubber St ene- Bare ball core R bb m bsttyrgine- Butadiene cog lymer gn s m carbonate 20 11 91' 118 6H6 F rmula C copolymer courilarone resm 3 Y Hardness Resilience Compres- Rebound steal'lne 1.5

3111 Benzoic acid 1 o 54 70 620 180 Mercaptobenzothiazolebisulfide 11,2 13 a a a a: stilft 3'2 35, 7 61 124 FORMULA E Natural rubber 100 It is seen from Tables HI and IV above that the hard- Zinc carbonate 12 ness of the rubber increases rapidly with an increased Kaolin 8 percentage of copolymer. The resilience of the rubber, Stearine 1 on the other hand, instead of steadily falling off with an Mercaptobenzothiazoledisulfide 1,5 increasing percentage of copolymer, passes through a Diphenylguanidine 8 slight maximum at a content of about 10% copolyrner, Sulphur 2.8

TABLE V Kaolin per 100 Rubber+Kaolin Bare ball core Finished ball parts of rubber in FormulaD Hard- Resil- Gonipres- Re- Weight, Oompres- Re- Weight,

ness ience, sion, bound, g. sion, bound, g. (Shore Percent inches .10 cm. inches .10 cm.

64 68 636 164 44. 2 610 126 67. 0 59 69 613 166 47. 9 453 126 61. s 66 66 436 158 53. 1 e14 134 66. 9 70 61 340 165 66. 4 251 140 69. 6 7a 60 320 164 67. 4 231 140 70. 6 73 58 262 160 60. 0 216 142 73. 0

TABLE VI m g Bare ball core Finished ball 0 Ooumarone per 6 parts of rubber-in FormulaD Hard- Resil- Oompres- Re- Weight, Oompres- Re- Weight,

ience, sion, bound, g. sion, bound, g. Percent inches .10 cm. inches .10 cm.

68 636 164 44.2 610 126 57 0 62 680 158 44. 6 515 58 2 62 680 130 44.6 663 115 67 s as 680 112 44.3 660 104 67 6 680 40 44.4 760 30 67 6 ,Ruhber-i- Bamhallcore ,Einished ball Oopolymer Oggglymergger 1310 v i r p Fbim fiia I? 'Hard Resil- 'o'ompres- "Re- Weight, Compres- Re- Weight,

ness. i. 11mm,. 51011,, ?bmfl,' .g. A1011, hound, g. Y (Shore Percent, finches .10, cm; es lll em. J

54; as v 636; 16L 44,2 .510 126' 57.0 61" 68 539 182' "-44.2 395 "140 67.6 70-, My :318 1822' 44.3 284. 144; 52.29 81, 52 g 163 r156 v 44.4 v .157; B8 67.8

As will appear from the above-tables, :the: balls are slightly harder-and havelessreboundtlramthe Exa le-- 5 I 6 f 'bare'ball cores. v I 20 I v I J a a v With amajor proportion of kao'hn incorporated in Natural-tubber..- m0 100 100 v v l. l lGopolymer (86%-s v12= ,30, 53 the rubber, balls may be'manufactured whlohhave-qulte z pgrbonate 1o .10 10 acceptable rebound and hardness charabtellstwsg asseen ggg g 2 a in Table "V. However, the "weight of "the balls becomes 1 7ige1raloiln v 5 5 g v .a I l a l too'great. If the' of the 'bans is to I? 125 Mercaptobenzothiazole .f 1-. 6 1.6 1. ,6 duce the weight, the hardness is red ce a the ,g gg

kg -73 -3 bound is also altered. With less kaolin 'the'ha rdness as "f l: I, 'well' as "the rebound become too :low. "Thu'stiit .is not 3 m I P f 89:11 7723 65:85 possible by incorporatingv kaolin. intherubber to arrive r g 5 v .at a ball which has the properlhardness,.,freboundeand ,Exampleu s I: g o 3.10 weight characteristics, without using an internal i-super- N I M 100 m0 100 a 11m r11 91"- v r, atmospheric pressure m -the ball. I eopolymermqo 41 Coumaroneresm (Table VI) ;wh1ch:hasz-approx1matel-y zinc carbonate. 1:5 the same specific gravity as I I 1:5 r greater amounts withoutvapprecialbly-affectmg"weight 5 I 5 .of "the 'ball. However, it reduces :thethardnessaand re- 7 136 i138 silience of the rubber mater'i'alandalsoeauses a redue B phur :tion of the rebound and hardness-characteristicsofthe 7 a i I p 0 3 311, Th r fore, such'resin, alone, ismtstiitatblehs a i' '"f" 70 30 rubber modifier for the present invention.

The specific gravity of "highstyrene-britadiene co:- polymer also differs insignifioantlyfromthat ofrubber. It increases the hardness of the rubber material .con- 'siderably, and reduces the resilience thereof. 'It lowers the rebound slightly butnot more thanl'raolin.

It can clearly be seen from Table 'VII, however that 'the rebound of the'balls'has a-.certainl-maximum which .lies at a higher proportionof thecopolymer component than the slight maximumwhich can be: found for the resilience of the rubber material.

As exemplified by Table VII, a'certain. amountnf kaolin may advantageously; be: incorporated in the rubber material. "Other well-known. fillers: may' also :beprese'nt. .It should be noted, however, zthat' such fillers-are not necessaryingredients in the rubber, whenhighstyrenebutadiene copolymers are added, but they are used as means for the purpose ofslightlyadjustingthe properties of the rubber and thebal-ls made theref'rom.

From Table VII it may be seeni'zthat the properties 10f thebare ball cores and those. ofathezfelt coveredballs do not vary quite in unison, withzvarying proportions-of copolymer in the rubber.. Thnsgwhilea sdttbtrllbecomes considerably less compressible through the felt covering, a hard ball does not change"'very much inrespect .of compressibility by the application ofthe felt covering. Similarly the rate of decrease of therbound, with increasing. percentages: of eopolym'er in rubber, is diminished by the felt-covering.- 1

Some further specific examples of rubber-copolymer compositions suitable for making tennis balls, having a gas filling of atmospheric pressure only, according to the present invention will now be given.

When using the extreme :rubber-copol-ymer composittionssrepresentednby the aboveExamples 5, 7,'8 and 1 0, considerable rdifliculti'es are experienced to have-the comrpressibility, rebound. and weight within: the limits re- ;qui-redzforltennis balls. This-is borneout by the figures in 'liables and IN, whichrefer 'to rubber-copolymer com- 'positibnsis'imilarto those disted :ajbove; I Where the rubberstructure of-the tennis balls is mad'e sin-omen: innerrubber-core ('not containing copol ymer) and an outer covering of rubbersopol'ymercornposition, proportion of copolymer will have to be slightly greater, as already pointed out, andfor this reason, the compositions :of Examples 5 and -8 -willhardly be practicabl'e insuclr caseywhile Examples 6, 7, 9 and 1 0 may perfomrxsatisfactorily'. Where a copolymer containing -86:%:sty1'ene=is: used atpracticalupper limit tor the prozportionlof-tlre copolymer'in thecomposition-appears to be about 45 5 It is I thought that :thezinvention: and its ad vantageswill .be understood from the lforegoingadescription and iti's apparentithat various changes may be made in the-J-forml, construction andarrangement-of the :p'ant's withoubdeparting; from the spiritaand. scope of. the invention 1m sacrificing its material advantages, the forms --hereinbefore described andlillustrated in ther-drawings beingmere- .ly preferred emhodimentszthereof.

' uHavingtthus. disclosedthe invention: What is claimedzis: 1.,A tennis. ball, comprising :a- .hollow :SlilllCtllIlfi-Jfif rubber, and a resinous highstyrene butadienecopolyrmer incorporated in at least a spherical annulus of said structure in a proportion of 10 to 45 parts thereof per 90 to parts of rubber, calculated on the basis of styrene in said copolymer, and a gas filling within said hollow structure at substantially atmospheric pressure.

2. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2% to 2% inches and a weight of 2 to 2% ozs, at least a core portion of said structure being of rubber, and at least a spherical layer of said core portion having. incorporated therein a resinous high styrene-butadiene copolymer in a proportion of 12 to 80 parts thereof, calculated on the basis of 85% styrene in said copolymer, per 100 parts of rubber to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 inches.

3. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2 /2 to 2% inches and a weight of 2 to 2% 02s., at least a core portion of said structure being of rubber, and .at. leasta spherical layer of said -core portion having incorporated therein 12 to 80 parts of a resinous high .styrene-butadiene copolymer, calculated on the basis of 85% styrene in said copolymer, and 10 to 47 parts of inorganic filler material per 100 parts of rubber, to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 inches.

4. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2 /2 to 2% inches and a weight of 2 to 2 1 02s., at least a core portion of said structure comprising rubber, 12 to 53 parts of a resinous high styrene-butadiene copolymer, calculated on the basis of 85 styrene in said copolymer, and 10 to 40 parts of inorganic filler material per 100 parts of rubber, .to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 in'ches.

5. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2 /2 to 2% inches and a weight of 2 to 2% 02s., at least a core portion of said structure comprising rubber, the outer spherical layer of said core portion having incorporated therein 30 to 53 parts of a resinous high vst-yrene-butadiene copolymer, calculated on the basis of 85% styrene in said copolymer, and 10 to 25 parts of inorganic filler material per 100 parts of rubber, to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 inches.

6. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2%. to 2% inches and a weight of 2 to 2 02s., at least a core portion of said structure comprising rubber, 16 to 79 parts of a resinous high styrene-butadiene copolymer, calculated on the basis of 70% styrene in said copolymer, and to 47 parts of inorganic filler material per 100 parts of rubber, to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 inches.

7. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2 /2 to 2% inches and a weight of 2 to 2 4 02s., at least a core portion of said structure being of rubber, the rubber in a spherical layer of said core portion having incorporated therein 41 to 79 parts of a resinous high styrene-butadiene copolymer, calculated on the basis of 70% styrene in said copolymer, and 15 to 32 parts of inorganic filler material per 100 parts of rubber, to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of copolymer, a surface layer of a material having surface characteristics equivalent to those of felt material, and a gas filling'within said hollow structure at substantially atmospheric pressure.

9. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2 /2 to 2% inches and a weight of 2 to 2 02s., at least a core portion of said structure being of rubber, the rubber in at least a spherical layer of said core portion having incorporated therein a resinous high styrene-butadiene copolymer in a proportion of 12 to parts thereof, calculated on the basis of styrene in said copolymer, per parts of rubber, to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 5 8 inches after a drop of 100 inches, and a surface layer of a material having surface characteristics equivalent to those of felt material.

10. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2 /2 to 2% inches and a weight of 2 to 2% 02s., at least a core portion of said structure being of rubber, the rubber in a spherical outer layer of said core portion having incorporated therein 30 to 5 3 parts of a resinous high styrene-butadiene copolymer, calculated on the basis of 85% styrene in said copolymer, and 10 to 25 parts of inorganicfiller material per 100 parts of rubber, to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 inches, and a surface layer of material hav ing slurface characteristics equivalent to those of felt maeria '11. A tennis ball, comprising a hollow structure at substantially atmospheric inner pressure having a diameter of 2% to 2 inches and a weight of 2 to 2 ozs., said structure having a spherical inner layer of rubber and a spherical outer layer of spongy rubber, the rubber of which the spongy rubber is formed having incorporated therein 30 to 5 3 parts of a resinous high styrene-butadiene copolymer, calculated on the basis of 85% styrene in said copolymer, and 10 to 25 parts of inorganic filler material per 100 parts of rubber to impart concurrently to said structure a deformation characteristic of 0.265 to 0.290 of an Inch under a pressure of 18 lbs. and a rebound characteristic of 53 to 58 inches after a drop of 100 inches.

References :Cited in the file of this patent UNITED STATES PATENTS 1,402,682 Takashima Jan. 3 1922 1,614,853 Schwartz Jan. 18, 1927 2,131,756 Roberts Oct. 4, 1938 2,452,999 Daly et a1. Nov. 2, 1948 OTHER REFERENCES Industrial and Engineering Chemist S t b pp 95.5457. ry, ep em er 1946,

India Rubber World, January 1948, pp. 487-491. Modern Plastics, February 1950, pp. 72-74. 

1. A TENNIS BALL, COMPRISING A HOLLOW STRUCTURE OF RUBBER, AND A RESINOUS HIGH STYRENE-BUTADIENE COPOLYMER INCORPORATED IN AT LEAST A SPHERICAL ANNULUS OF SAID STRUCTURE IN A PORPORTION OF 10 TO 45 PARTS THEREOF PER 90 TO 55 PARTS OF RUBBER, CALCULATED ON THE BASIS OF 85% STYRENE IN SAID COPOLYMER, AND A GAS FILLING WITHIN SAID HOLLOW STRUCTURE AT SUBSTANTIALLY ATMOSPHERIC PRESSURE. 